1. Field of the Invention
The present invention relates to an illumination device provided with a rotating panel for switching color of illumination light.
2. Description of the Related Art
Conventionally, printers have been proposed which are provided with a printing head using a light shutter that comprises, for example, a PLZT. Furthermore, printing heads have been proposed which are provided with an illumination device having a rotating panel to modulate light emitted from a light source into light of each color red (R), green (G) and blue (B) and direct the modulated light to the light shutter.
The general construction of a full color printer provided with a PLZT printing head is described below. FIG. 10 briefly shows a partial construction of the full color printer. Part of light emitted from a halogen lamp 21 as a light source is directed to an illumination device 24 by an aluminum pipe 23. Only a color wheel 11 is shown in the drawing as a rotating panel forming a structural element of the illumination device 24, and other structural elements which are not illustrated include a drive source for driving the rotation of the color wheel 11, and a housing for accommodating the color wheel 11. Reference number 22 refers to a light-transmitting heatproof filter for blocking the heat generated by the halogen lamp 21.
The color wheel 11 of the illumination device 24 is provided with a plurality of glass panels as transparent members sequentially arranged in a direction of rotation of the color wheel 11. The light emitted from the halogen lamp 21 passes through the pipe 23 and is modulated sequentially to R, G, B by the respective glass panels via the rotation of the color wheel 11. Details of the construction of the color wheel 11 and the illumination device 24 are described later.
Reference number 25 is a fiber bundle comprising a lot of plastic fibers. The light modulated by the illumination device 24 (i.e., color wheel 11), is transmitted within the fibers to a polarizer 26. The fiber bundle 25 has a circular cross section on the color wheel 24 side, and the fibers are arranged in a linear array on the polarizer 26 side.
Only the light oscillating in a predetermined direction is transmitted through the polarizer 26. The light which is transmitted through the polarizer 26 further passes through an integrator 27 to suppress dispersion. A shutter array 28 is a member in which a plurality of PLZT elements as optical shutters is arranged in the form of an array, and these shutters are turned ON and OFF via the application of a voltage to the PLZT elements. The light passing through the shutter array 28 arrives at an analyzer 29, and only the light oscillating in a predetermined direction passes through the analyzer 29. The light passing through the analyzer 29 forms an image on a color photographic paper 31 as a recording medium via a lens 30. A full color image is printed on the photographic paper 31 by regulating an amount of R, G, B light via the shutter array 28.
The color wheel 11 is described below. FIG. 11 is a top view of the color wheel 11. FIG. 12 is a cross section view on an A-Axe2x80x2 plane in FIG. 11. Glass panels 1r, 1g and 1b are each 1 mm thick, and are processed such that these have a fan-like shape with an interior angle of 60xc2x0. The glass panels 1r, 1g and 1b are optically coated so as to modulate white light transmitted therethrough to R (1r), G (1g), B (1b) light, respectively. That is, the glass panels 1r, 1g and 1b have mutually different light transmitting characteristics. The glass panels 1r, 1g and 1b respectively comprise a pair of elements, for a total of six elements.
A top flange 2 and a bottom flange 3 fixedly hold the glass panels 1r, 1g and 1b. The top flange 2 and bottom flange 3 made of aluminum both have a disk-like shape. The bottom flange 3 is provided with an opening 3a on its center. A wall 3b is formed on one side of the bottom flange 3 along a circumferential edge of the opening 3a. 
The glass panels 1r, 1g and 1b are locked by the top flange 2 and the bottom flange 3 as described below. The bottom flange 3 is disposed with a surface on which the wall 3b is formed facing upward, and the glass panels 1r, 1g and 1b are placed on the bottom flange 3 and abut the wall 3b, such that like color panels face one another across the center. Then, the top flange 2 is overlaid onto the bottom flange 3 so as to hold the glass panels 1r, 1g and 1b between the two flanges, and the top flange 2 is fixed to the bottom flange 3 via adhesive or screws or the like.
By the way, in the full color printer provided with the PLZT printing head of the aforesaid construction, the color wheel 11 must rotate at approximately 12000 rpm to attain a desirable printing speed. When rotating at such a high speed, however, the color wheel 11 is subject to extremely large centrifugal force which rapidly causes damage to the glass panels 1r, 1g and 1b. 
Gaps may be generated at mutual connective regions of the glass panels 1r, 1g and 1b of the color wheel 11 due to measurement discrepancies during manufacture. Light may disadvantageously leak from these gaps, and adversely affect printing.
Furthermore, another problem occurs when the color wheel 11 rotates. FIG. 13 is a side section view of a conventional illumination device 24. The color wheel 11 is accommodated in a dustproof housing 8. A motor 10 as a drive source is provided in the opening 3a of the bottom flange 3 of the color wheel 11 (refer to FIG. 12). The color wheel 11 is rotated within the housing 8 via the drive provided by the motor 10. The light emitted from the halogen lamp 21 (refer to FIG. 10) enters the color wheel 11 through an entrance window (not illustrated) in the housing 8, passes through the glass panel 1r (or 1g, or 1b), and is emitted from an exit window (not illustrated) in the housing 8.
As shown in the drawing, the housing 8 has two mutually opposing surfaces parallel to the rotational plane of the color wheel 11, i.e., a bottom surface of the housing body 8a and the back surface of the housing cover 8b. The color wheel 11 is disposed within these two surfaces so as to be closer to the housing body 8a. When the color wheel 11 is rotated, the area near the rotational axis and the area of the exterior circumference have different circumferential speeds, such that an airflow is generated from the center of the color wheel 11 toward the exterior side in a space (B) between the color wheel 11 and the housing body 8a (indicated by an arrow 12 in the drawing).
The space (B) is subject to a low air pressure condition due to this airflow 12, which produces a force in a downward direction (indicated by an arrow 14 in the drawing) on the color wheel 11. The rotational balance of the color wheel 11 is disrupted under the effects of this downward force, and rotational stability is lost. These effects are particularly pronounced when an air motor is used as the drive source.
An object of the present invention is to eliminate the previously described disadvantages by providing an improved illumination device.
Another object of the present invention is to provide an illumination device provided with a rotating panel capable of high-speed rotation.
Still another object of the present invention is to provide an illumination device which does not leak light from a rotating panel.
Yet another object of the present invention is to provide an illumination device capable of stable rotation of a rotating panel.
These objects are attained by providing an illumination device comprising:
a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and
a frame member arranged on an exterior circumference of the rotating panel for supporting the plurality of transparent members.
In this illumination device, the transparent members are hard to be damaged even when subjected to centrifugal force via the rotation of the rotating panel because the transparent members are supported by the frame member.
In this illumination device, the frame member may be adhered to the transparent members via adhesive. In this case, even when dimension discrepancies occur during the manufacture of the transparent members and the frame member, the looseness is absorbed by the adhesive.
These objects are further attained by providing an illumination device comprising:
a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and
a light shield member for sealing between adjacent transparent members.
In this illumination device, even when gaps occur at the connective regions between transparent members, light is prevented from leaking by the light shield member.
These objects are further attained by providing an illumination device comprising:
a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotating panel; and
a housing for accommodating the rotating panel, said housing having two mutually opposing surfaces parallel to a rotational plane of the rotating panel, and having an airflow inlet near a rotational axis of the rotating panel on a surface nearer to the rotating panel among the two surfaces.
In the space between the rotating panel and the surface nearer to the rotating panel in this illumination device, airflow is generated from the center of the rotating panel toward the exterior side thereof, but there is no change in air pressure in this space because external air inflows to the space from the airflow inlet.
In this illumination device, a plurality of the airflow inlets may be disposed at equal intervals on a circumference centered on a position corresponding to a rotational axis of the rotating panel. In this case, air flowing from the airflow inlet is not deflected so as to maintain equal air pressure in the space.
In this illumination device, a filter may be provided at the airflow inlet. In this case, external air flowing into the housing is clean because the filter traps dust etc.
In this illumination device, the housing also may be provided with an airflow outlet near an exterior circumference of the rotating panel on the surface provided with the airflow inlet. In this case, there is no change in air pressure in the space because exterior air flows into the housing from the airflow inlet, and air inside the housing is discharged from the airflow outlet.
In this illumination device, the housing may be provided with a pipe connecting the airflow inlet and the airflow outlet. In this case, there is no change in air pressure in the space because an airflow is generated circulating through the pipe and the space.
A plurality of the airflow inlets and the airflow outlets may be arranged at equal intervals on respective circumferences centered on a position corresponding to a rotational axis of the rotating panel. In this case, a constant air pressure is maintained in the space because the inflow and discharge of air from the airflow inlet and the airflow outlet are not deflected.
These objects are further attained by providing an illumination device comprising:
a rotating panel including a plurality of transparent members having different light transmitting characteristics sequentially arranged in a rotational direction of the rotational panel; and
a housing for accommodating the rotating panel,
wherein the rotating panel is accommodated in the housing so as to maintain equal distance from two mutually opposing surfaces of the housing parallel to a rotational plane of the rotating panel.
In this illumination device, an equal airflow is generated in both spaces between the rotating panel and the two surfaces of the housing, and pressure is hard to be exerted on the rotating panel due to deflection of air pressure because the spacing between the rotating panel and the two surfaces of the housing are equal.